Field of the Invention
The present invention relates to a method of manufacturing a rectangular tube having a stepped portion for connection formed at an end thereof.
Description of the Background Art
The rectangular construction tubes used for fences or barriers have been generally assembled in such a fashion that a plurality of rectangular tube members each having a predetermined length are formed, and thereafter, the plurality of formed rectangular tube members are butted one another, and the formed rectangular tube members abutting one another are fixed through connection members. However, the use of connection members has caused increase in component count and cost. Furthermore, the use of such connection members has sometimes caused an undesirable appearance.
For the purpose of reducing cost, there has been proposed a method of: radially reducing an end of one rectangular tube; and inserting the radially reduced end into an end (non-radially reduced end) of another rectangular tube so as to connect the rectangular tubes (see patent document 1).
For example, patent document 1 proposes a method of: radially reducing an end of one round tube through the use of a die; connecting the radially reduced end with an end (non-radially reduced end) of another round tube; and thereafter, forming the connected round tubes into a rectangular tube by roll forming.
In the roll forming described in patent document 1, a plurality of roll stands equipped with rolls each having a predetermined dimension are installed around the connected round tubes. Such connected round tubes are inserted into the rolls so as to form a rectangular tube having a predetermined dimension. Rectangular tube members manufactured by such a method are used for fences or barriers.